Hot stretching of polyacrylonitrile yarns with draw point located on feed roller



Sept. 26, 1961 w. MAIER ET AL 3,001,236

HOT STRETCHING OF POLYACRYLONITRILE YARNS WITH DRAW POINT LOCATED ON FEED ROLLER Filed July 16 1958 INVENTORS. KURT BERNKLAU.

WA LTB? MA/ER,

W ATTORNEYS 3,001,236 HOT STRETCHING F POLYACRYLONITRILE YARNS WITH DRAW POINT LOCATED ON FEED ROLLER Walter Maier and Kurt Bernklau, Dormagen, Germany,

assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed July 16, 1958, Ser. No. 748,966 Claims priority, application Germany July 26, 1957 1 Claim. (CI. 18-48) This invention relates to the stretching of polyacrylonitrile yarns, and more particularly an improved process of stretching such yarns.

It is known that yarns or films consisting of polyacrylonitrile or of copolymers with a minimum content of about 85% of polyacrylonitrile can be stretched to about 4-10 times their length by heating them to a temperature of at least 100 0., preferably 130-180 C. and stretching them in this condition.

The stretching process is generally carried out by either sliding the yarn continuously over a heated surface or by running the yarn in one to several convolutions around a heated roller, whereupon the yarn heated in this Way is drawn off by one or more rollers at greater peripheral speeds.

In the hot stretching of yarns of polyacrylonitrile or of copolymers containing at least 85% of polyacrylonitrile, it has been shown that a yarn having equal thickness at all places cannot readily be produced by the known processes. Polyacrylonitrile yarns are spun from a solution and stretched with a residual content of solvent. Since the residual content of solvent varies at the various parts of the yarn on the spinning spoo1for example the outer layers and marginal zones of the yarn package contain less solvent due to evaporation than those portions of the yarn which are nearer to the spool-the yarn offers a smaller resistance to the stretching in proportion as it contains more solvent at one or other place. The same applies to the diflerent contents of solvent of the different capillary filaments at one and the same place on the yarn. For these reasons, it is not possible with the known processes to obtain a uniform yarn suitable for textile purposes at a working speed which is sufficiently high for carrying out the process commercially.

It is therefore an object of the invention to provide a process by which polyacrylonitrile yarns can be stretched at economical speeds.

A further object is an improved process of stretching polyacrylonitrile yarn which produces a stretched product of even thickness along the entire length of the yarn and of all capillary filaments in the yarn.

A further object is the provision of a stretching apparatus which will avoid the disadvantages of the conventional stretching machines.

Still further objects will become apparent as the following specification proceeds.

The objects are accomplished by heating the yarn or the like on a rotating roller which is brought to a temperature of 100-200 C., preferably 130-180 C. and stretching the yarn before being drawn off the said roller, so that the point of stretch formed is located on the roller itself and can change its position thereon, by guiding the stretched yarn over a slightly curved frame. which is atent 3,001,236 Patented Sept. 26, 1961 heated to a temperature which differs by no more than 50 C. from the temperature of the rollers.

Referring now to the single figure of the accompanying drawing, a polyacrylonitrile yarn 1, prepared by extrusion of a solution of the polymer in dimethyl formamide into an evaporative medium, whereby the dimethyl formamide is removed and a yarn containing only a small amount of solvent is formed, is led from a suitable source of supply, such as a yarn package, on to a heated roller 2 with the roller pin 3 and wound around this roller for several times. After leaving this roller, the yarn travels over the frame 4 which is also heated and which can be pivotally arranged. The yarn, upon leaving the frame 4, passes over an idler roll 5 and then without slippage about a second positively driven roller 6 which rotates at a speed of about 4-10 times the peripheral speed of the heated roller 2. Cooperating with said roller 6 is a displacement guide. The stretched yarn is then collected on a rotating bobbin 7.

Example A yarn obtained by dry spinning a co-polymer of of acrylonitrile and 5% of vinyl acetate from a dimethyl formamide solution, which then still contains on average 6% of dimethyl formamide and consists of 30 capillary filaments with a total count of 360, based on the dry weight of the yarn, is led by means of a roller pin 3 six times around the roller 2 which has a diameter of 3 inches, is heated to 150 C. and runs at a peripheral speed of ft./min. On drawing off the yarn, the point of stretch is formed on the roller at an average distance of 2 inches from the point at which the yarn is drawn off the roller. Immediately after the stretched yarn has been drawn ofi the heated roller, it travels on to the slightly curved frame 4 having a length of 7 inches and heated to 165 C., whereupon it is drawn off by means of the roller 6 with a speed of 600 ft./min. The yarn has a high degree of uniformity as regards its count, and has a uniform dyeing capacity when worked up into fabrics.

We claim:

Process for the hot stretching of yarns consisting of a copolymer of 95% of acrylonitrile, 5% of vinylacetate and an average solvent content of about 6% dimethylformamide, wherein the yarns are heated in contact with a positively driven supply roller which has a surface temperature of about C. and a peripheral speed of about 100 ft. per minute, then led over a slightly curved frame having a surface temperature of about C. and then to a stretching roller which is positively driven at a peripheral speed about 6 times as high as the speed of said supply roller, whereby the point of stretch is localized on the surface of the supply roller and permanently remains thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,289,232 Babcock July 7, 1942 2,611,923 Hume Sept. 30, 1952 2,768,057 Friederich Oct. 23, 1956 2,811,409 Clapp et al. Oct. 29, 1957 2,821,458 Evans Jan. 28, 1958 2,859,472 Wincklhofer Nov. 11, 1958 

